As Scream pointed out, few hosting service will allow you to run mod_perl. He's a very good programmer, I think.

PHP is a lot easier for non-programmers to come to grips with, so the market will be much bigger. Perl scripts like GT produces run the risk of being labelled "For Perl Programmers only". If you want your market to include all the part-time, non-programmer Web masters out there, then you need to make sure that your scripts have an excellent and easy to use admin interface.
samantha